The leaders of the United States and Iran have spoken by telephone in the highest level conversation between the two estranged nations in more than three decades.
The historic conversation between Barack Obama and new Iranian President Hassan Rouhani is the first time the heads of state of the two countries have spoken directly since 1979.
Speaking to reporters at the White House, Mr Obama said he and Mr Rouhani discussed their ongoing efforts to reach an agreement over Iran's nuclear programme.
"I reiterated to President Rouhani what I said in New York: while there will surely be important obstacles to moving forward and success is by no means guaranteed, I believe we can reach a comprehensive solution," he said.
Mr Obama said it was a unique opportunity to make progress with Tehran over Iran's nuclear ambitions, an issue that has isolated it from the West, the BBC reports.
He said the two leaders had instructed their teams to work as swiftly as possible to seek a solution.
Earlier, Mr Rouhani said he wanted talks with major powers on Iran's nuclear programme to yield results in a short period of time.
At the United Nations General Assembly in New York, Mr Rouhani said the atmosphere between his country and the United States was quite different from in the past.
He said he was pleased with what he had achieved in New York and his success had exceeded his expectations.